The major objective of this proposal is to examine the role of the nucleoside transport system in relation to adenosine's action in cardiovascular and pulmonary function. The role of the nucleoside adenosine in the physiological regulation of cardiac function, particularly coronary blood flow and myocardial contractility, is now well known. The assessment of this role of adenosine has been centered around its quantitation, the enzymatic activities involved in its metabolism and studies of the adenosine receptors. The possible relevance of the nucleoside transport system, an integral part of the adenosine inactivation mechanism, to adenosine-mediated autoregulation of the heart or to its defects in cardiac function has received little attention. Preliminary studies have indicated that recognition sites for [3H]nitrobenzylthioinosine, a potent inhibitor of nucleoside transport, exist in the heart, lung and various vascular beds. With [3H]nitrobenzylthioinosine as a radioligand probe, studies will be done using radioreceptor binding assays as the primary experimental tool to characterize and determine the role and regulation of these recognition sites in vascular and pulmonary function. Potential compounds which may physiologically modulate these recognition sites will be identified and characterized. The effects of physiologic and pharmacologic intervention on the plassticity of the recognition sites will also be investigated. The chief models to be used in these studies include guinea pig cardiac and pulmonary membranes, isolated blood platelets, bovine aortic and pulmonary arterial endothelial cells. The isolation of guinea pig cardiac and pulmonary endothelial cells is an important long term goal of this project. The data derived from these studies will be used to develop an hypothesis that will enhance understanding of the role of the nucleoside transport system and adenosine in cardiovascular and pulmonary function, organ blood flow and hemostasis.